Ion exchange recovery of oxazole from acrylonitrile compositions



United States Patent 3,541,131 ION EXCHANGE RECOVERY OF OXAZOLE FROMACRYLONITRILE COMPOSITIONS Claude Darcas and Claude Tcherkawsky,Saint-Avold,

France, assignors to Ugine Kuhlmann, Paris, France, a corporation ofFrance No Drawing. Filed May 23, 1967, Ser. No. 640,492

Claims priority, applicggirirslirance, May 27, 1966,

Int. 01. civic 121/32 US. Cl. 260-465.?) 4 Claims ABSTRACT OF THEDISCLOSURE This invention relates to the recovery of nitrogen containingheterocyclic compounds such as oxazole from nitrile compositions whichhave been purified by standard methods after production by catalyticreaction of ethylenic hydrocarbons with ammonia and oxygen in the vaporphase.

Nitriles including acrylonitrile may be produced by the vaporphase-reaction of ethylenically unsaturated hydrocarbons such aspropylene with ammonia and an oxygen containing gas such as air in thepresence of known catalysts. The product as produced contains a varietyof impurities and even after purification, for example by distillation,small quantities of these impurities may remain. The presence of theseimpurities have a deleterious effect on the quality of the productssubsequently prepared from the nitriles. For example, certain of theseimpurities adversely eifect the quality of polymers prepared fromacrylonitrile. It is these nitrile compositions referred to herein aspartially purified nitrile compositions with which this invention isprincipally concerned.

Various methods have been devised for the separation of these impuritiesby distillation, but the volatility of the impurities is often so closeto that of the nitrile to be purified that separation by distillation isvery complicated and costly. These problems are especially significantin the case of acrylonitrile which is an extremely important industrialchemical.

Heterocyclic compounds, especially those which are Weakly basic due tothe presence in the ring of at least one nitrogen atom, as in the azolegroup of oxazole or isoxazole, are amongst the harmful impurities whichhave been found in industrial reaction products of the above describedclass. These compounds, especially oxazole, are themselves industriallyimportant as starting materials or intermediates in the production ofvarious commercial products, especially pharmaceutically usefulcompounds.

A method of separating and recovering ozazole and related heterocycliccompounds of low basicity while avoiding the complications and cost ofprior distillation procedures would be a significant advance in the art.Such a method has now been discovered.

In accordance with this invention nitriles such as acrylonitrilecontaining oxazole and similar nitrogenous 3,541,131 Patented Nov. 17,1970 bases are purified by contacting the nitrile composition with acationic ion exchange resin in the acidic form. The selected resinshould be substantially insoluble in the nitrile to be purified. Theprocess of the invention is applicable to the purification of nitrilecompositions containing from 0.5 parts per million to 5% by weight ofheterocyclic compounds or even a higher percentage of these compounds.

The preferred cationic ion exchange resins for use in this invention aresulfonated polystyrene resins crosslinked with varying amounts ofdivinyl benzene. Several commercial embodiments are available. Theygenerally difier amongst themselves in particle size, porosity, extentof cross-linking, etc. Suitable resins which may be employed arecommercially available under the trademarks, Duolite C 20, Allasion CS,Dowex 50, Amberlyst l5, Amberlite 200, Amberlyst XN 1005, Lewatite8-100, Lewatite S-ll5, Relite CPS, and the like.

The invention is preferably practiced in a continuous manner by passingthe composition to be purified through a resin bed at a flow rate offrom about 4 to about 60 volumes of composition per volume of resin perhour. A preferred rate consistent with achieving the desired purity withcommercial quantities of composition at reasonable cost is from 10 to 30volumes per volume of resin per hour. When operating within thesedefined ranges substantially all of the hererocyclic, nitrogenous baseis removed to produce a commercial nitrile of especially high purity. Atrates appreciably below 4, the process is very slow without acompensating improvement in results. The degree of purity of the nitrileproduct varies inversely with the rate of throughput as this rateincreases above 60, although useful results can be achieved at ratesappreciably above this value.

The invention, as stated above, includes as one of its aspects therecovery of the nitrogenous base which is absorbed on the resin, and theregeneration of the resin to permit its reuse. The regeneration of theabsorptive capacity of the resin is an especially valuable object ofthis invention.

Various procedures have been proposed for regenerating cationic ionexchange resins which have exchanged their hydrogen ions for basicmaterials. Resins which have exchanged hydrogen ions for sodium orcalcium ions are regenerated by contact with an acid of sufiicientlyhigh concentration. In general, acids which are of greater acidity thanthe resin will displace a base from the resin. The original basiccompound can also be eluted by bathing the resin with a solution of astronger base which displaces the weaker base. Subsequently the resin isregenerated through Washing with an acidic compound capable of producinga salt by reacting with the stronger base on the resin.

A disadvantage of these various regeneration procedures is the largeconsumption of the elution reagents and the large quantities of waterwhich are utilized to wash the resin so as to remove even traces of acidor base which might remain in the resin and contaminate the product tobe purified. With cationic resins it is even necessary in washing theresins to utilize distilled water or water from which both cations andanions have been removed so as to avoid premature and unnecessaryremoval of hydrogen ions, especially by alkaline or alkaline earth ions.The cost of regeneration has markedly limited the use of cationic ionexchange resins to the extent that they are not utilized in manyoperations where they could otherwise be advantageously employed.

It has been discovered in accordance with this invention that it ispossible to regenerate cationic resins which have been saturated or atleast partially so with weakly basic substances, by a facile andeconomic procedure which does not employ alkaline or acidic reagents andpermits the recovery of the absorbed basic substances from the resins.The process comprises elution of absorbed substances such as oxazole andthe like by washing with deionized water. This is a most surprising andvaluable discovery since it had previously been believed that theregeneration of the resins required the use of a substance capable ofproviding ions.

The washing can be effected with relatively cold water, but an elevatedtemperature, preferably the temperature of boiling water is moreeffective, and requires a smaller quantity of water. In a particularlypreferred aspect of the invention the hot water wash is combined withentrainment of the desorbed substance by steam followed by condensationto permit recovery of the substance. Accordingly, the regeneration canbe effected at temperatures of from about 20 C. to about 100 C.

The process of the invention allows substantially complete regenerationof the initial fixation capacity of the resin so as to permit removal ofthe basic substance from successive nitrile compositions, and reuse ofthe same mass of resin for a practically unlimited number ofabsorption-desorption cycles.

In summary, the regeneration technique of this invention does not employacidic and/or basic reagents which complicate the installation andincrease the costs. In addition it combines the advantages of asubstantially quantitative and yet easy recovery of materials which areconsidered undesirable impurities in the original nitrile compositions,but which are, nonetheless, valuable for the synthesis of other valuablecompounds by known methods.

The following non-limiting examples are given by way of illustrationonly and illustrate the process of this invention as utilized to purifya partially purified acrylonitrile monomer produced by the vapor phasecatalytic reaction of propylene, ammonia and air. The acrylonitrilecontains 85 parts per million by weight of oxazole and 0.3% by weight ofwater. The oxazole content of the acrylonitrile is determined by gasphase chromatography utilizing apparatus equipped with a very sensitiveflame ionization detector which responds to an oxazole content on theorder of 0.5 part per million.

EXAMPLE 1 A glass tube with an inside diameter of mm., and a height of500 mm. is used to contain the cationic resin column. A plug of glasswool is placed at the base of the column to prevent the resin fromwashing through. A three way stop-cock at the head of the column allowsthe column to be shut off or the shifting of the material feeding thecolumn from the nitrile to deionized water. A similar three waystop-cock at the bottom of the column permits directing of the efiiuentinto the receiver flasks or permits the entry of water or steam into theresin column to loosen it, if necessary, or to regenerate it.

The composition to be purified is fed to the column with a meteringpump. In this example the flow is downward through the column, but itcould be an upward fiow.

Amberlyst 15, a sulfonated cationic ion exchange resin of the classspecifically described above is employed. The particle size is fromabout 0.3 to 1 mm. The resin is utilized in the acid form. A total of7.5 g. of dry resin are weighed out and allowed to swell in distilledwater. In the swollen state the resin occupies a volume of approximately25 cc. The tube is filled with water and the moist, swollen resin isslowly dropped in while vibrating the tube to avoid formation ofcavities in the resin column. The column is then drained.

The partially purified acrylonitrile to be further purified is meteredinto the column at a rate of approximately 500 cc. per hour. At thisrate the resin bed is operated continuously in a flooded condition.

One liter fractions of eluate are analyzed chromatographically asdescribed above. It is found that up to the sixth liter, the efiluentcontains no trace of oxazole so that 6 liters of acrylonitrile have beenpurified to the point where very sensitive instruments are not capableof detecting the presence of oxazole. The seventh liter containsapproximately 10 ppm. of oxazole. The breakthrough point of the oxazoleunder these conditions, therefore, is between the sixth and seventhliter of acrylonitrile.

The operation is continued until the oxazole concentration in theefiluent is approximately equal to that in the infiuent, i.e. ppm. Thisrequires the collection of approximately eleven liters of acrylonitrile.At this point the resin is saturated with oxazole. The operation is thendiscontinued and the column is drained.

This example illustrates the purification of acrylonitrile to the pointof complete saturation of the resin. In industrial practice, conditionswould be adjusted so that the column would be taken out of operationjust before the breakthrough point so that only acrylonitrile containingno detectable oxazole would be produced. Under these conditions theresin would be only partially saturated and regeneration using theprocedures of the following examples would progress more quickly.

EXAMPLE 2 After loosening the saturated resin column produced in theprevious example by the upward passage of an air stream, the resin iswashed with water at room temperature. The washing rate is about 300cc./hr.

With a column in which the resin is saturated with oxazole the directionof the wash fiow may be either the same as, or opposite to that of theacrylonitrile fiow. If the resin is only partially saturated, bestresults are obtained by washing in the direction opposite to the flow ofacrylonitrile. In this particular experiment the direction of flow ofthe acrylonitrile and of the deionized water is the same.

It is found by chromatographic analysis of the eluate that 80% of theoxazole originally on the column is eluted with one liter of water and93% with three liters of water.

After collection of three liters of eluate, regeneration is discontinuedand the column is ready for a new purification operation.

EXAMPLE 3 A resin saturated with oxazole by the procedure of Example 1is regenerated with deionized water, using the EXAMPLE 4 The procedureof Example 3 is repeated using water at a temperature of from C. to C.It is found that only 550 cc. of deionized water is required to remove98% of the oxazole. After the passage of only one liter of water no moreoxazole is detectable in the eluate.

EXAMPLE 5 A total of 7.5 g. of Amberlyst 15 is saturated with oxazole inaccordance with the procedure of Example 1. The resin is first loosenedby passing cold deionized water upwards through the column. The threeway stop-cock is replaced by an extender which forms an expansion vesselof 30 mm. diameter and 70 mm. height. The upper porresin. Aftercondensation of 250 cc., no more oxazole is detectable in thecondensate.

The oxazole is recovered from the combined condensate fractions bydistillation in an eflicient plate column.

EXAMPLE 6 Procedures similar to those of Examples 1 and 2 are carriedout through 50 successive cycles of absorption, elution andregeneration, each cycle comprising the passage of acrylonitrilecontaining 85 p.p.m. of oxazole through 7.5 g. of Amberlyst 15 withpractically complete elimination of oxazole and regeneration of theresin.

Chromatographic analysis of the eluates from successive cycles shows noelimination of the absorption capacity of the resin. Its breakthroughpoint remains between 6 and 7 liters of acrylonitrile for each cycle.

No deterioration of the Amberlyst 15 particles is apparent bymicroscopic examination. No increase in the number of fine particles isdetectable by granulometric analysis.

What is claimed is:

1. A process which comprises the removal of a compound selected from thegroup consisting of oxazole and isoxazole from acrylonitrilecompositions produced by vapor phase reaction between propylene, ammoniaand oxygen in the presence of a catalyst and containing at least one ofsaid compounds by contacting said composition with a water-moistcationic ion exchange resin in the acid 6 form, the same being the onlyion exchange resin used in the process, whereby at least one of saidcompounds is absorbed on said resin and thereafter recoveringacrylonitrile from said composition.

2. A process as in claim 1 in which contact is efiected by passing thenitrole composition through a column of cationic ion exchange resin inthe acid form at a flow rate of from about 4 to about 60 volumes ofnitrile per volume of resin per hour.

3. A process as in claim 1 in which the flow rate is from 10 to volumesof nitrile per volume of resin per hour.

4. A process as in claim 1 in which the resin is a sulfonatedpolystyrene cross-linked with divinyl benzene.

References Cited UNITED STATES PATENTS 7/1948 Blann 260465.9 XR 8/1964Leach 260-4659 FOREIGN PATENTS 1,131,134 10/1968 Great Britain.

